The loose structure of European oak makes whisky mature faster and with high amounts of tannins. Nuts, apple, apricot and spice flavours, such as nutmeg, are very easy to find in European oak.
American oak has a closed cellular structure that makes whisky mature more slowly. Vanilla, butter, coconut, banana and toasted bread are typical flavours found in American oak.
Bourbon whisky needs to be matured in brand new casks to have vanilla, butter and coconut flavours.
Sherry wine is from Jerez, Spain in the region forming a triangle between Sanlúcar de Barrameda、El Pueroto de Santa María and Jerez de la Frontera. There are two types of Sherry wine, sweet and dry. According to the development of Flor, dry Sherry wines include Fino, Manzanilla、Oloroso、Palo Cortado and Amontillado. Moscatel and Pedro Ximénez (PX) are sweet Sherry wines, which add a spirit in order to stop fermentation and increase the alcohol content. Maturation in ex sherry casks brings dark chocolate and caramel flavours to whisky.
Toasting and Recharring the surface of the casks increases the complexity and multi-layered flavours in the whisky. American cooperages use four different types of recharring: light, medium, heavy and the "alligator effect". The alligator effect is the heaviest charring of all.
The new make will be filled into barrels for maturation, with the interaction between the two being the very essence of each whisky’s character formation. There are different minimum maturation periods of whisky globally.